Novel compositions for improved concrete performance

ABSTRACT

A method for the preparation of industrial-scale concrete installations with improved compression strength, curling, cracking and cracking characteristics, the method comprising the addition of nanosilica particulate, and more preferably, colloidal amorphous silica, having specific size and surface area characteristics to a concrete mix after water has been added to the mix and the mix has been agitated.

PRIORITY CLAIM

This application claims priority to Provisional Application 62/761,064,filed on Mar. 9, 2018; Provisional Application 62/761,393. Filed on Mar.22, 2018, and Provisional Application 62/765,597, filed on Sep. 1, 2018.

Concrete has been the basic element of construction since ancient times.Depending upon the type, concrete can have enough compressive strengthto withstand the rigors of the elements and continuous public use withlittle structural degradation over time. Essential to its usefulness isthe pourable rheology of water-containing mixtures of uncured concrete.Pourability of concrete enables structural shaping, such as for example,with a mold or other constraint, prior to curing into a hard form. Waterfunctions in both the shaping and curing of concrete. However,heretofore, it has been necessary to carefully manage the water whichgives rise to the pourability of concrete; too much or too little waterin the concrete at any time during curing can negatively affect theconcrete curing process, leading to a structurally compromised concreteproduct.

Water in curing concrete generally has three important functions. First,water is required for the hydration of the dry cement. The hydrationreaction (curing) is the concrete-forming reaction (C—S—H formingreaction): water participates in a reaction by which the bonds areformed which give concrete its compressive strength. Theoretically, theconcrete with the greatest compressive strength is formed when thehydration reaction goes to completion. In reality, the hydrationreaction generally proceeds to a significant degree during the firststages of curing, but is limited at later times by evaporation of waterfrom the surfaces of the curing concrete. Concrete hydration can begreatly affected by ambient conditions such as wind speed, relativehumidity and temperature. Thus, concrete can “dry” even though it isonly partially cured. If the concrete surface dries out prematurely,hydration can be incomplete, giving a surface that is both porous andweak. In order for concrete to reach its full-strength potential, it isgenerally required that water be in place continuously for extendedperiods of time, often for days. In practice, concrete is seldom curedto its full-strength potential.

A second function of water is to aid in pourability of concrete. Uponthe addition of water to the cement, but before hydration takes place ona large-scale, much of the water that will ultimately participate inhydration is already associated with the additives and calcium hydroxidein the concrete. Water in excess of this associated water generallybenefits flowability of concrete, with more “extra” water generallycorrelating with a greater flowability of the concrete.

In general, it is thought in the industry that even relatively smallamount of such extra water is detrimental to the concrete product.Environmental conditions (wind, relative humidity and temperature) cancause the surface of the slab to dry faster than the interior. Internalwater is often trapped interiorly. A degree of hydration begins with theaddition of water to the cement, and shortly after pouring, hydrationcan be well underway. The trapped water can escape to the surfacethrough capillaries formed by the relatively dried, partially curedsurface. The trapped water may instead form reservoirs inside the curingconcrete, resulting in voids in the cured concrete product. Bothcapillaries and reservoirs can compromise the compression strength ofthe resultant cured concrete. They also enable environmental water toenter the concrete during its lifetime of service, allowing the concreteto be degraded by freeze damage and other water-mediated damageprocesses.

Furthermore, it is thought that water that does not participate inhydration (i.e., water that does not combine chemically with theconcrete) essentially adds volume to the poured concrete, and the lossof this water during drying generally results in some degree ofshrinkage of the concrete during curing. Nevertheless, the concrete mustbe workable. Thus, the inclusion of the optimum amount of water suchthat hydration (curing) and workability are maximized, while shrinkageand structural damage to the concrete during hydration/drying isminimized remains a delicate balancing act, made all the more difficultby environmental factors.

A third function of water is to enable finishing of partially curedsurfaces which may also be desiccated due to evaporation. Surfaces whichdry prematurely are generally difficult to finish. It is a normalpractice to add water to such surfaces to facilitate strike-off, closingand finishing. Added water can penetrate the surface, particularly whencapillaries are present. Such water generally leaves the concrete slowlyover an extended period, often even when the concrete appears dry. Oftenfurther steps, such as sealing or steps which require securingcomponents such as floor tiles or carpeting to the floor are affected bythe slow release of finishing water. For example, it is not unusual foradhesives to fail within a short time of floor installation due to theslow emission of water. This water is often primarily finishing water.Even when water is added, the finishing machines often must be operatedat higher settings in order to effectively finish a surface which haspartially dried.

The use of additional cementitious materials in concrete to improveconcrete properties, such as, for example, water impermeability,compressive strength and abrasion resistance, is well-known. Varioustypes of particulate silica, such as, for example silica fume, have beenused in concrete as additional cementitious materials to improvewater-impermeability and compressive strength. A general problem withsilica is that it can raise the water demand of a concrete formulationsuch that the likelihood of capillaries and void formation during curingis increased due to the higher likelihood of significant bleedwater. Inorder to reduce bleed water, it is common in the art to use relativelylarge amounts of silica fume (5 to 10 percent by weight of cementitiousmaterials), with water minimized or carefully rationed to relatively lowamounts, such as, for example, below a ratio of about 0.5 by weight ofwater to cementitious materials. (Design and Control of ConcreteMixtures, Sixteenth Edition, Second Printing (revised); Kosmatka, StevenH.; pg. 156). Such low amounts of water are generally below what isrecommended by the cement manufacturer, and can significantly impair therheology of the concrete, causing it to be difficult to pour or work.

BRIEF DESCRIPTION OF THE INVENTION

Surprisingly it has been found that the use, in poured concreteinstallations, of nanosilica (i.e., amorphous silica having particleswith an average particle size of less than about 55 nm, and in someembodiments, less than about 7.8 nm, or, in other embodiments, betweenabout 5 and about 55 nm, or between about 5 and about 7.9 nm; and havinga surface area in the range of from about 300 to about 900 m²/g, or inother embodiments, from about 450 to about 900 m²/g, in amounts suchthat it is present in the concrete in a weight ratio in the range offrom about 0.1 to about 4 ounces amorphous silica per 100 lbs of cement(i.e., not including water, aggregate, sand or other additives) canresult in a significantly lower rate of water loss during curing thanconcrete which is hydrated in the absence of such amorphous silica.Thus, the surfaces of newly-poured, partially-cured concrete of theinventive method remain easily workable for longer periods than those ofconcrete prepared by other methods, and are less sensitive toenvironmental conditions which ordinarily speed evaporation. Bleedwater,curling, cracking and shrinkage are generally greatly reduced.Compressive strength of the resultant cured concrete is generallysignificantly increased. Remarkably, important to the realization of thebenefits of the invention is the introduction of the silica to theconcrete mix after the water and other dry components have been mixedsuch that the dry components are thoroughly wetted. The introduction ofthe silica at an earlier stage, such as prior to the wetting, generallydoes not give a significant reduction in bleedwater, cracking andshrinkage, and may in fact be worse in such aspects than non-silicacontrols. The foregoing holds true even if there is an improvement incompressive strength with respect to non-silica controls.

A concrete is disclosed which comprises small-particle-size,high-surface-area amorphous silica, used in much smaller proportions tothe cement than generally used in the industry for structural purposes:only about 0.1 to about 4 ounces per hundred weight of cement mix(“cwt”). In an additional aspect, the improved concretes are prepared bya process-specific addition of the silica. These improved concretes canbe prepared using the standard amount of water recommended by the cementmanufacturer, or even water in excess of the recommended amount, withoutsignificantly compromising compressive strength. Such a result is trulysurprising. Despite the use of such water amounts, little or nobleedwater is observed during curing. The formation of capillaries andvoids is minimal or even essentially completely suppressed, and morewater is retained in the concrete during curing, allowing more water toparticipate in curing over an extended period of time, and compressivestrength, both early (3 day) and, particularly late (28 day) is greatlyimproved.

Despite their allowance for relatively high amounts of water, thelow-silica concretes have improved compressive strength and abrasionresistance, among other improved characteristics. An improvement incompressive strength, is surprising, considering the small amounts ofsilica employed, while known methods use much larger amounts to achievegains which are, in some cases, significantly less. Furthermore, largeimprovements in concrete abrasion resistance have generally not beenobserved with the use of silicas such as, for example, silica fume, evenin the larger amounts usually used. (id, pg. 159). The low-silicaconcretes, described herein, give profound improvement in abrasionresistance as measured by test ASTM C944. (Note that with regard to theforegoing standard, the version employing a 22 pd, 98 kg load was usedin all references to the standard herein.) Standard concretes (i.e., notcomprising the high-surface-area amorphous silica taught infra) can havea value of in the range of from about 2.5 to about 4.0 grams of loss.The low-silica concretes taught herein can have an ASTM C944 value is aslow as 1.1 grams of loss or less.

Even more remarkably, the specific steps of the process for mixing thecomponents to form the cement mix are important for the realization ofthe increased water retention, compressive strength and workability ofthe newly-poured, partially-cured concrete surfaces. Essentially all ofthe amorphous silica is added after the combination of some oressentially all water and the dry ingredients (for example, cement mix,aggregate, sand), within a mixing machine, such as, for example, aReady-mix to be used in the mixing stage (i.e., prior to the actualpour). By “essentially all of the water,” it is meant that water whichis part of the amorphous silica formulation, such as, for example, waterinvolved in creating a colloidal suspension of the amorphous silica,generally being much less than the water added to the concrete mix, isnot included within the meaning of “essentially all.” It is particularlyconvenient to add the small particle-size silica after (or in someembodiments, with) a final portion of water (i.e., “tailwater”) prior tofinal mixing and pouring. The breaking of water addition into twoportions id particularly convenient with the use of a Ready-mix, in thatthe second portion can be used to rinse remnant dry components from nearthe mouth of the drum down into the bulk.

That small particle silica is more effective after tailwater addition isunexpected. The general thinking in the art is that the addition ofsilica to concrete has heretofore been thought generally effective evenif it is added to the mix of cementitious materials prior to theaddition of water. However, it has been found on the scale required forconstruction of building slabs, footings and other large scale concretepours, such that mixing and pouring equipment such as Ready-mixes areused, the addition of the small amount of small-particle-size silica, asdescribed herein, has been demonstrated, as indicated herein, to be muchmore effective when added after the quantity of water, or, in preferredembodiments, with or after a second portion of water (“tailwater”) toconcrete which has been wetted and, optionally, mixed for a period oftime, as disclosed herein, than when it is added before the water, orwith the portion of water used to wet the cementitious materials.

The amorphous silica is added after the water, cement mix and solids(aggregate and sand) are mixed, such as for example, with a Ready-mix orother mixer. The formation of capillaries and reservoirs can be reducedor eliminated. The benefits of the invention can generally be obtainedeven when the concrete mix contains significant amounts of water inexcess of that required by the concrete in order to fully hydrate it(cement mixes generally have a recommended amount of water to give theconcrete which can be fully hydrated according to the manufacturerspecification). Concrete having water equal to, or even in excess of theamount required for full hydration, or recommended by the cement mixmanufacturer, are preferred.

While silica of larger sizes has been shown to improve compressivestrength of concrete, it is well-known that silica has a waterrequirement and as size is decreased and surface area is increased, theamount of water required by the concrete increases. Thus, the perceptionin the art is that there is a tension between 1) decreasing silicaparticle size and 2) keeping water content low enough such that theformation of capillaries and voids are minimized. Thus, it is thoughtthat at small particle sizes, a risk exists that the water requirementwould override the structural benefits provided by silica. Illustratingthis fact, the applicants have found that if the prescribed amorphoussilica is added to the cement or concrete mix at other points in thepreparation of the pourable concrete mixture, such as, for example, atany time prior to relatively complete mixing of water and cement mix(before or with the water which wets the cement mix, the resultingpoured concrete can exhibit significantly more capillaries, voids and/orresulting surface bleed water than if the amorphous silica is addedafter complete mixing of the water and cement mix. Thus, it is trulysurprising that if the silica is added, (preferably as amorphouscolloidal silica or precipitated silica) at a point after the cement andwater have been completely mixed, the formation of capillaries and voidsis reduced or eliminated, water evaporation is slowed, and newly-poured,partially-cured surfaces are generally easily worked, often without theaddition of finishing water. In general, it would be expected that somedegree of benefit can be observed when the silica is added after thewater even if complete mixing of the water and cement mix has not takenplace.

The success of delayed addition of nanosilica is particularly surprisingin light of what has been discovered about how factors such asnanosilica particle size and surface area affect concrete properties,most notably compressive strength, when introduced as colloidal silicainto concrete-forming mixtures. A summary of some findings in the art,the most recent findings of which the inventors only become aware aftertheir own experimentation, is as follows. The use of colloidalnanosilica (silica having average particle sizes of less than about 100nm, and particularly silica having average particle sizes of less thanabout 10-15 nm) in concrete-forming mixtures has been fraught withissues pertaining to compressive strength, among other properties, ofthe resulting concrete. For example, past studies have shown that largerparticle-size silica, such as, for example, silica fume (about 145 nm)generally has a positive effect upon compressive strength in a widerange of particle sizes and loadings. However, smaller silica particleshave a much more complicated correlation with compressive strength.Recent studies have shown that nanosilica particles tend to agglomeratein colloidal solutions. (Non-nano-sized silica particles, such as, forexample, silica fume, have larger surface potentials, and are much lessinclined to agglomerate.) The studies further show that suchagglomerates, when introduced into concrete-forming mixtures and notsubsequently sufficiently dispersed, such as, for example, by agitation,can become spaces in the final concrete product which are devoid ofconcrete matrix structure, negatively affecting compressive strength andother properties. However, the studies also show that the extensivesurface area afforded by nanosilica for pozzolanic reaction, being muchgreater (by more than one order of magnitude, often several) than thatof non-nano-sized silica, causes the C—S—H matrix-forming reaction toexperience competition from reactions at the silica surface. As aresult, the availability of a large amount of surface area can result ina weaker C—S—H matrix, resulting in lower compressive strength. Thus, inthe search for nanosilica loading parameters which increase compressivestrength, there can be a tension between 1) the persistence ofaggregates in the concrete-forming mixture, and 2) agitation of theconcrete-forming mixture or the application of other modes ofdispersion, such that the aggregates are reduced or eliminated, butresulting in a surge in the amount of exposed silica surface area.

Setbacks were encountered in the inventor's attempts to use nanosilicain the field. It was found that silica loadings which clearly producecompressive strength gains in the lab when prepared by standardprocedures such as ASTM 305-06 often failed to give compressive strengthgains when used in standard fashion in a larger-scale process subject tothe preparation constraints of an industrial pour, e.g. a Readymixprocess. Furthermore the concrete was often rheologically compromised,having poor pourability, as well as often exhibiting greater bleedwater,cracking, curing and shrinkage than a silica-free control.

Such a procedural dependence for the same loading levels of nanosilicacould be considered unexpected because the apparent differences are inscale, as well as increased time to complete component mixing associatedwith the Readymix. One of skill in the art may not expect the processeswhich affect compressive strength to occur on the relatively brieftimescale involved in the initial mixing of the concrete components,such that the differences in mixing times would affect compressivestrength. This is especially true given that test cylinders are taken atpour time; i.e., differences in measured compressive strength could beargued to be not even partially attributable to larger bulk size of slabvs. size of sample.

Furthermore, upon extensive experimentation, the addition of the silicalate in the mixing process as described infra was found to restore thecompressive strength-boosting effect of nanosilica. This was anunexpected result because much, if not almost all of the mixingagitation has taken place by the time the nanosilica is finally added.Thus, any aggregates are less likely to be completely dissipated intothe concrete mix, and would theoretically weaken the concrete asdescribed above. In general, it has been found that on a constructionscale, adding the colloidal nanosilica after the addition of water givesa concrete mixture which is more pourable and a concrete product whichof increased compressive strength, pourability, and wear resistance; aswell as decreased cracking, curling and shrinking with respect tostandard addition samples and silica-free control samples.

LIST OF TABLES

Table 1—A summary of experimental results taken in accordance with theprocedure described in Example 3 and referred to in the analysispresented therein.

DETAILED DESCRIPTION

A concrete mix is created from components comprising quantities of a) adry cement mix; b) water; c) amorphous silica; and d) aggregate and orsand.

Thy cement mixes generally have a recommended water content which givesa water/cement ratio providing a concrete mix which has a combination ofdesirable pouring and curing characteristics. In some cases, therecommended water content encompasses a range of water contents. Asindicated infra, the initial water content of concrete mix prior topouring can give rise to issues during curing and finishing which reducethe quality of the resulting concrete installation (slab, footing,etc.). It is common for water-reducing measures, such as the use of“water-reducers” and superplasticizers to be employed in the interestsof reducing water-mediated structural flaws in the cured concrete. Itshould be noted that while the benefits of the present invention shouldbe evident in circumstances in which the water content is being reducedbelow that recommended by the manufacturer, the present invention can beused to give the inventive concrete in situations in which the waterincluded in the concrete mix is equal to or greater than the amountspecified by the manufacturer of the dry cement mix. Water-reducers inthe concrete mix are generally unnecessary.

Thus, in a broad aspect, the cement mix and the water are present in theconcrete mix are present in the mix in the following proportions:A quantity of water; and a quantity of dry cement mix, said cement mixcharacterized by:i) a manufacturer suggested water/cement ratio value; wherein saidsuggested ratio falls in the range of from about 0.35 to about 0.65; andwhereupon combination with the quantity of water, the water/cement ratiois greater than the value corresponding to about 10% less than thesuggested value but less than the value corresponding to about 30% morethan the suggested value; orii) a manufacturer suggested water/cement ratio range, having an uppervalue and a lower value, and whereupon combination with the quantity ofwater, the water/cement ratio is greater than the value corresponding toabout 10% less than the lower value and not greater than the valuecorresponding to about 30% more than the upper value; oriii) an amount such that, whereupon combination with the quantity ofwater, the water/cement ratio is in the range of from about 0.35 to0.65;

The benefits of the invention are generally expected to be manifest withthe use of commercially useful types of Portland cement. The cement mixis one or more of the types commonly used in construction, such as, forexample, Portland cements of Types I, II, III, IV and V.

The quantity of water above is added to the cement mix. This quantity isinclusive of all water which is combined with the concrete mixcomprising at least the cement mix, except water introduced with thesilica in the case of water-containing formulations such as colloids,dispersions, emulsions, and the like. As further detailed below, thewater can be combined with the concrete mix comprising at least thecement mix in multiple portions, such as, for example, the addition of asecond portion of water (for example, “tailwater”) after a first portionof water has been combined with the concrete mix and agitated for atime. Note that water is sometimes applied to the surface of concreteafter it has partially cured, to prevent the premature drying of thesurface, which could result in shrinkage, as well as later difficultiesin working and finishing. This “finishing” water is not included withinthe quantity of water. In other embodiments, the water/cement ratio isin the range of from about 0.38 to 0.55, or, in more specificembodiments, in the range of from about 0.48 to about 0.52, or in therange of from about 0.38 to about 0.42.

In a more preferred embodiment, in reference to i), ii), and iii),above, the water and cement mix are present in the concrete mix in theproportions wherein upon combination of the quantity of dry cement mixwith the quantity of water, the water/cement ratio is: equal to orgreater than the suggested value, but not greater than the valuecorresponding to 30% more than the suggested value; or

equal to or greater than the upper value of the suggested range, but notgreater than the value corresponding to about 30% more than the uppervalue; orat least 0.35, but not greater than 0.65.

Particle size of amorphous silica is particularly important. Largerparticle sizes, such as will be found in micronized silica, generally donot reduce the formation of capillaries and voids to the degree seenwhen amorphous silica sized as prescribed herein is used in theprescribed amounts. The inventive concrete mix comprises a quantity ofamorphous nanosilica, which is preferably present in an amount in therange of from about 0.1 to about 7.0 ounces per hundredweight of cement(cwt) in a), and having particle sizes such that the average silicaparticle size is in the range of from about 1 to about 55 nanometers,and/or wherein the surface area of the silica particles is in the rangeof from about 300 to about 900 m²/g, or in other embodiments, from about450 to about 900 m²/g.

Amorphous silica from various sources is generally suitable as long asit is characterizable by the particle size and surface area parametersabove. Nonlimiting examples of suitable amorphous silica includecolloidal silica, precipitated silica, silica gel and fumed silica.However, colloidal amorphous silica and silica gel are preferred, andcolloidal amorphous silica is most preferred.

In further embodiments, the silica particle size is in the range of fromabout 5 to about 55 nm. Preferred are particles with average particlesize of less than about 25 nm, with average particle size of less thanabout 10 nm more preferred, and average particle size of less than about7.9 nm even more preferred. A preferred weight proportion in theconcrete is from about 0.1 to about 3 ounces of amorphous silica per 100lbs of cement (not including water, aggregate, sand or other additives).A more preferred weight proportion in the concrete is from about 0.1 toabout 1 ounces of amorphous silica per 100 lbs of cement (again, notincluding water, aggregate, sand or other additives). Even morepreferred is about 0.45 to about 0.75 ounces of amorphous silica per 100lbs of cement (again, not including water, aggregate, sand or otheradditives). Surprisingly, above about 3 to about 4 ounces of theamorphous nanosilica per 100 lbs cement mix, the concrete mix can becomedifficult to pour or work, and compressive strength can suffer greatly,even with respect to non-silica controls. Otherwise, amounts above about1 ounce per 100 lbs cement generally give decreasing compressivestrength gains with respect to the preferred range of about 0.45 toabout 0.75 ounces of amorphous silica per 100 lbs cement. The preferredrange given is the most economically feasible range, i.e., above that,the compressive strength gains are less per additional unit of silica,and cost of silica per unit increase of compressive strength may causethe cost of the concrete to become prohibitive.

Amorphous silicas having surface areas in the range of from about 50 toabout 900 m²/gram are preferred, with about 150 to about 900 m²/grammore preferred, and about 400 to about 900 m²/gram even more preferred,and 450-700 m²/gram or 500-600 m²/gram even more preferred. Amorphoussilica with an alkaline pH (about pH 7 and above) is preferred, with apH in the range of from 8 to 11 being more preferred.

In yet another embodiment, the amorphous silica is provided by the useof E5 INTERNAL CURE, an additive available commercially fromSpecification Products LLC, which contains about 15 wt % amorphoussilica in about 85 wt % water. The silica particle characteristics arean average particle size of less than about 10 nm (measured by BETmethod), and a surface area of about 550 m2/g. In one embodiment, theweight proportion of E5 INTERNAL CURE to cement is in the range of fromabout 1 to about 20 ounce of E5 INTERNAL CURE to 100 lb cement (notincluding water, sand, aggregate or other additives). More preferablythe weight proportion of E5 INTERNAL CURE to cement is in the range offrom about 1 to about 10 ounces of E5 INTERNAL CURE to about 100 lbcement (not including water, sand, aggregate or other additives). A morepreferred weight proportion of E5 INTERNAL CURE to cement is in therange of from about 1 to about 5 ounces of E5 INTERNAL CURE to about 100lb cement, with about 3 to about 5 ounces of E5 INTERNAL CURE to about100 lb cement (not including water, sand, aggregate, or other additives)even more preferred. Surprisingly, the use of more than about 20 ouncesof E5 to about 100 lb cement (again, not including water sand, aggregateor other additives) can cease to be of benefit in that additionalbeneficial water or compressive strength benefits may not be observed ormay be minimally observed. The resulting concrete mix may be difficultto pour, and any resulting concrete may be of poor quality. Note thatthe quality of the concrete diminishes with the distance from thepreferred range of about 3 to about 5 ounces per 100 lb cement, but thecompressive strength may still be improved over that in the absence ofthe E5 INTERNAL CURE colloidal amorphous silica. In preferredembodiments the colloidal silica added to the concrete mix is in therange of from about 40 to about 98 wt % silica, with 60 to 95 wt %preferred and 70 to 92 wt % more preferred, and 75 to 90 wt % even morepreferred.

Aggregate and sand can generally be used in the inventive concrete inamounts as known in the art for construction purposes. In oneembodiment, a quantity of aggregate and/or a quantity of sand is usedsuch that they total an amount in the range of from about 400 to about700 wt % bwoc, In general, a concrete mix is prepared with componentscomprising cement mix, water, and, preferably, a quantity of aggregateand sand (sometimes referred to in the art as “large aggregate” and“small aggregate,” respectively). It is permissible for the concrete mixto comprise only one of the two, such as only sand or only aggregate,but it is preferred the mix comprise at least a quantity of each. Sandand aggregate can contribute to the silica content of the cementmixture, and thus they can affect (i.e., raise somewhat) the waterrequirement of the concrete mix. Generally, most types of aggregatewhich are appropriate for the use to which the concrete is to be put canbe used. Included are larger aggregates such as coarse, crushedlimestone gravel, larger grades of crushed clean stone, and the like, aswell as smaller aggregates such as the smaller grades of crushed cleanstone, fine limestone gravel, and the like. Likewise, many types ofsand, such as pit (coarse) sand, river sand and the like can be used.Generally, in concrete applications, “coarse sand” is preferred to “softsand,” which is known to be more appropriate for use in mortars.However, soft sand may generally be expected to have a different waterrequirement than coarse sand when used in concrete preparation. As isknown in the art, weight-bearing applications may require largeraggregate, such as coarse, crushed limestone. Such larger aggregate ispreferred for poured concrete applications, particularly for use inpoured building slabs are the larger aggregates, such as, for example,coarse crushed limestone gravel and larger grades of crushed cleanstone, and pit sand.

The proportion of aggregate and sand, taken together, based on weight ofcement (bwoc) is preferably in the range of from about 2000 to about4000 lbs per yard of dry cement mix (in the range of from about 520 toabout 610 lbs per yard, or more preferably from about 560 to about 570lbs per yard, even more preferably, about 564 lbs per yard). Morepreferred is a combined proportion of aggregate and sand in the range offrom about 2700 to about 3300 lbs per yard of dry cement mix. Morepreferred is a range of from about 2900 to about 3100 lbs per yard ofdry cement mix. In another embodiment, the weight of aggregate and sandis between 50 and 90 wt % based upon the weight of the concrete, with arange of from about 70 to about 85 wt % preferred. The relative amountsof aggregate and sand are not critical, but are preferably in the rangeof from about 20 wt % to about 70 wt % sand based upon the combinedweight of the sand and aggregate, with about 40 wt % to about 50 wt %sand preferred.

It has been discovered, especially in commercial scale pours, that eventhe small amounts of amorphous nanosilica required to effect thedisclosed benefits, when added to the cement mix prior to the water, canbe detrimental to the pourability of the concrete mix, as well as thequality of the resultant concrete, even rendering the concreteunsuitable. The process of the present invention generally includes thesituation in which at least a portion of the quantity of water is addedprior to the addition of the quantity of amorphous nanosilica, with atleast a time period of agitation between the additions to distribute thewater prior to the addition of the amorphous silica. In practice, somewater may be added later in the preparation process, if desired. Forexample, it is known to add water in two (or more) portions, such as thepractice of adding a portion as “tailwater” after the addition andagitation of a first portion. In one embodiment, the amorphous silica isadded as a colloidal silica with a second portion of water. In apreferred embodiment, the colloidal silica is added after the additionof water which has been added in two portions, with agitation after theaddition of each portion.

Thus, more generally, the quantity of water can be added in its entiretyor added in portions comprising an initial portion, comprising in therange of from about 20 wt % to about 95 wt % of the quantity of water,and a tailwater portion, comprising the remainder; wherein the initialportion of water is combined with the quantity of cement mix and theaggregate/sand components to form a first mix; and wherein the amorphoussilica is added to a mix comprising the quantity of cement mix, theaggregate/sand components and the initial portion of water to form asecond mix. Even more preferred is an initial portion comprising in therange 35 to about 60 wt % of the quantity of water.

(The below three situations (i.e., “situation 1”, “situation 2” and“situation 3”) correspond, respectively to i) the addition of the silicaafter the addition of the tailwater; ii) the addition of the silicabefore the addition of the tailwater; and iii) the co-addition of thesilica with the tailwater.)

In embodiments with split water addition, wherein the tailwater is 1)added to the first mix; or 2) added to the second mix; or 3) co-addedwith the amorphous silica to the first mix, wherein the amorphous silicaand the tailwater are, optionally, intercombined; and wherein 1) thefirst mix is agitated for a time t₁₁ prior to the addition of thetailwater, for a time t₁₂ after the addition of the tailwater but beforethe addition of the amorphous silica, and for a time t₁₃ after theaddition of the amorphous silica; or 2) the second mix is agitated for atime t₂₁ prior to the addition of the amorphous silica, for a time t₂₂after the addition of the amorphous silica but before the addition ofthe tailwater, and for a time t₂₃ after the addition of the tailwater;or 3) the second mix is agitated for a time t₃₁ prior to co-addition ofthe amorphous silica and the tailwater, and whereupon the concrete mixis then agitated for a time t₃₂.

In situation 1), in which the second portion of water (tailwater) isadded to a concrete mix comprising a first portion of water, thequantity of cement mix and the sand/aggregate components, t₁₁ ispreferably in the range of from about 2 to about 8 minutes, with about 3to about 6 minutes more preferred, and at a mixing speed (such as forexample, in a Ready-mix) preferably in the range of from about 2 toabout 5 rpm. Time t₁₂ is preferably in the range of from about 0.5 toabout 4 minutes, with a more preferred range of from about 1 to 2minutes, at a mixing speed in the range of from about 2 to about 5 rpm.Time t₁₃ is preferably in the range of from about 2 to about 10 minutes,with a range of from about 5 to about 10 minutes more preferred, with arelatively high mixing speed at a rate in the range of from about 12 toabout 15 rpm. After the high rate mixing, the rate can be lowered to arate in the range of from about 2 to about 5 rpm for a time, such as,for example, a transit time to a pour site. Transit time standards areset by the American Concrete Institute. For example, the concrete mustbe poured within 60 minutes of the end of high-rate mixing if thetemperature is 90 F or greater, and within 90 minutes if the temperatureis less than 90 F.

In situation 2), in which the second portion of water (tailwater) isadded to a concrete mix comprising a first portion of water, thequantity of cement mix and the sand/aggregate components, and theamorphous silica, t₂₁ is preferably in the range of from about 2 toabout 8 minutes, with about 3 to about 6 minutes more preferred, and ata mixing speed (such as for example, in a Ready-mix) preferably in therange of from about 2 to about 5 rpm. Time t₂₂ is preferably in therange of from about 0.5 to about 2 minutes, with a more preferred rangeof from about 0.5 to 1 minutes, at a mixing speed in the range of fromabout 2 to about 5 rpm. Time t₂₃ is preferably in the range of fromabout 2 to about 10 minutes, with a range of from about 5 to about 10minutes more preferred, with a relatively high mixing speed at a rate inthe range of from about 12 to about 15 rpm. After the high rate mixing,the rate can be lowered to a rate in the range of from about 2 to about5 rpm for a time, such as, for example, a transit time to a pour site.As noted above, transit time standards are set by the American ConcreteInstitute.

In situation 3), in which the tail water is co-added with the amorphoussilica to the first mix, wherein the amorphous silica and the tailwaterare, optionally, intercombined, t₃₁ is preferably in the range of fromabout 2 to about 8 minutes, with about 3 to about 6 minutes morepreferred, and at a mixing speed (such as for example, in a Ready-mix)preferably in the range of from about 2 to about 5 rpm. Time t₃₂ ispreferably in the range of from about 2 to about 10 minutes, with arange of from about 5 to about 10 minutes more preferred, with arelatively high mixing speed at a rate in the range of from about 12 toabout 15 rpm. After the high rate mixing, the rate can be lowered to arate in the range of from about 2 to about 5 rpm for a time, such as,for example, a transit time to a pour site. As noted above, transit timestandards are set by the American Concrete institute.

In another embodiment, the entire quantity of water is added to thequantity of cement mix and the aggregate/sand components to form a mix,whereupon said mix is agitated for a time t_(a) prior to the addition ofthe amorphous silica, whereupon the concrete mix is then agitated for atime t_(b) prior to pouring. The addition of the entire quantity ofwater at once is useful in the case of wet batch processes. Time t_(a)is preferably in the range of from about 2 to about 8 minutes, withabout 3 to about 6 minutes more preferred, and at a mixing speed (suchas for example, in a Ready-mix) preferably in the range of from about 2to about 5 rpm. Time t_(b) is preferably in the range of from about 2 toabout 10 minutes, with a range of from about 5 to about 10 minutes morepreferred, with a relatively high mixing speed at a rate in the range offrom about 12 to about 15 rpm. After the high rate mixing, the rate canbe lowered to a rate in the range of from about 2 to about 5 rpm for atime, such as, for example, a transit time to a pour site. As notedabove, transit time standards are set by the American ConcreteInstitute. While benefits of the invention would generally be observedin the case of a single addition of water, in practice, the two-portiondivision of water is generally adhered to. After the agitation of aconcrete mix comprising a first portion, the use of a second portion hasthe advantage of washing down into the Ready-mix remnants ofinsufficiently mixed cement mix from near the mouth of the barrel.

The concrete mixture can be prepared in a wet (“central mix”) or dry(“transit mix”) batch situation. In wet batch mode, the dry componentsare mixed with the quantity of water followed by the amorphous silica togive a concrete mix, in one of the ways indicated above. The mix isagitated as above or introduced into a Ready-mix and agitated therein asindicated above. Essentially, the wet and dry batch situations aresimilar except that part of the procedure for a wet batch is performedoutside of the Ready-mix (for example, at the plant). Dry batching(“transit mix”) is somewhat preferred. For example, 40 plus or minus20%, or, in further embodiments, plus or minus 10% of the total quantityof water to be utilized in the preparation of the concrete mix, sand andcoarse aggregate used in the batch is loaded into a Ready-mix. Thecement mix, coarse aggregate and sand are mixed together and loaded intothe Ready-mix. The remaining water is then loaded into the Ready-mix.Once the dry components and the water are completely mixed, theamorphous silica is added, and the mixture is mixed for 5 to 10 minutes.The mixing preferably takes place at relatively high drum rotationspeeds, such as, for example, a speed in the range of from about 12 toabout 15 rpm. Once the higher-speed mixing has occurred, the batch canthen be poured. However, it is permissible to have a period of timebetween the higher-speed mixing and pouring, such as transport time tothe pouring site. In general, as long as the concrete is mixed at lowerspeeds, such as, for example, about 3 to about 5 rpm, a time between thehigh-speed mixing and the pouring of in the range of from about 1 toabout 60 minutes is permissible.

In one embodiment, it is particularly convenient to add the silica to aReady-mix, which contains the water, cement and other dry components,once the Ready-mix has arrived at the pour site. It has further beenfound that after the amorphous silica has been added, theconcrete/silica mixture should be mixed, prior to pouring, for a time,most preferably at least from about 5 to about 10 minutes. However,other periods of time may be permissible with respect to at leastpartially obtaining the benefits of the invention.

The benefits of the invention can be expected in commercially usedvariants of the foregoing process, as long as the amorphous silica isadded at the end, after the mixing together of the dry components andthe first and second portion of water (or with the second portion ofwater), and the silica-added mixture is mixed for a time as specifiedherein prior to pouring.

The concrete mix is then poured to form a concrete installation. In apreferred embodiment, the concrete mix is formed and agitated in thecontext of an industrial scale pour, such as the preparation of footingsor slabs. In an additional embodiment, the concrete mix is created withand within equipment which holds the mix as it is being created, andwhich also has the capacity to agitate the mix, such as, for example, aReady-mix.

One advantage of the present inventive process is that water in concreteformation, such as for example, a slab, formulated according to thepresent invention, appears to be immobilized in the formation ratherthan lost to evaporation. The likely fate of much of this water is toparticipate in hydration at extended periods of time rather than formcapillaries and voids. Thus, it is expected that, regardless ofthickness, concrete slabs, walls and other formations will display areduction or lack of voids and capillaries, and a correlative gain incompressive strength. Concrete formation having improved structure andcompressive strength with thicknesses up to about 20 feet can be formedwith the concrete of the present invention.

An advantage of the present inventive process is that poured concreteare less damaged by drying caused by environmental conditions, such astemperature, relative humidity and air motion such as wind. For example,concrete of good quality can be produced at wind speeds as high as 50mph, temperatures as high as 120° F. and as low as 10° F., and relativehumidities as low as 5% and as high as 85% or even higher.

The compressive strength of the concrete formed by the method of thepresent invention is generally increased with respect to concrete formedby methods which are similar or, preferably, the same save for theaddition of silica after the mixing of the water, cement mix and fillermaterials (aggregate, sand and the like). “Similar” or “the same”applies to environmental conditions such as wind speed, relativehumidity and temperature profile, as well as other environmentalfactors, such as shading or heat radiating surroundings with respect tothe assessment of increase in compressive strength. Factors within thepourer's control, such as mixing times and parameters, pouringparameters (i.e., slab dimensions) are more easily accounted for. Anincrease in compressive strength is preferably assessed from pours whichare identical except for the addition of the amorphous silica. In apreferred embodiment, the assessment is made from pours which areprepared from identical amounts of identical ingredients, simultaneouslybut in separate Ready-mixes, poured side-by-side, at the same time, butusing separate Ready-mixes. Such pours are “substantially identical.”

The increase in compressive strength can be in the range of from about 5to about 40% or even more, based upon the compressive strength of thenon-silica-containing pour of a pair of substantially identical pours.In more commonly observed embodiments, the compressive strength increaseas assessed through substantially identical pours is in the range offrom about 10 to about 30%.

The concrete of the present invention can generally be used inapplications which require poured concrete, such as, for example, slabs,footings, and the like. An advantage of the present invention is thatthe concrete prepared therefrom is generally of increased resistance towater penetration, and can thus be used in poured applications which areparticularly prone to moisture exposure and the associated damage, suchas footings.

As indicated infra, the present invention involves the discovery thatnanosilica, when added to a concrete mix, preferably as a colloidalsilica, after the addition of at least a portion of water, gives acement having an improved compressive strength among other improvedproperties, such as abrasion resistance and water permeability.

The additive concrete components such as sand and aggregates of sizeswhich are used in the art can generally be used in the concrete of thepresent invention without destroying the benefits provided by thepresent invention.

Thus, it is possible to utilize a concrete, comprising of ample waterfor hydration, pouring and working, in the preparation of concrete whichgenerally lacks the deficiencies otherwise associated with concrete fromconcrete having high amounts of water of transport. The inventivecompositions result in concrete which retains water such that exposedsurfaces are less likely to dry prematurely than concrete which have nothad amorphous silica added. The relative water retention effect isobserved even in ambient conditions under which the surface wouldordinarily be predisposed to desiccate. Concrete can thus be pouredunder a broader range of environmental conditions than standardconcrete. Surfaces can thus be finished with reduced amounts of surfacewater, or even, in some cases, without adding surface water.

Remarkably, shrinkage is reduced with respect to concrete containingcomparable amounts of water. More remarkably, the compressive strengthis increased. This result is generally obtained even though the concretecontains amounts of water of transport that would risk capillary andvoid formation in absence of amorphous silica.

Without desiring to be bound by theory, it is surmised that theamorphous silica may immobilize the water during curing such that thewater is prevented from migrating, retarding evaporation as well ascapillary and void formation. Surprisingly, the immobilization does notprevent the water from participating in long term, extended hydration,which gives the unexpected increase in compressive strength.

An overarching benefit of the present invention is the ability not touse excess water in the curing reaction (hydration) due to generallylosing the water to evaporation. Such a benefit can be obtained even inthe case of concrete which are poured having water levels which are lessthan theoretically required for full hydration of the concrete, as wellas at water levels which are in excess of that theoretically requiredfor hydration.

A problem with existing concrete preparation and pour processes is therisk taken when a pour is done in less than optimum conditions. Asindicated infra, relative humidity, wind speed and temperature, amongother environmental factors, routinely compromise standard pours becauseof their effect on the water levels at various locations on and withinthe concrete. This can occur even when the amount of water includedcomplies with the recommended amount of water specified by the cementmix manufacturer, whether it is a recommended range of values or asingle specified optimum value. The present invention enables theoperation at the cement manufacturer's suggested water contents with areduced risk of water-related issues. These suggested values generallycorrespond to the amount of water which would be required to enable thehydration reaction to proceed to an acceptable degree, or in some cases,to completion. In the practice of this invention, use of water in theamounts specified by the cement manufacturer is preferred. However, thepresent invention also reduces the risk of water issues with respect toother processes even when the water content deviates from that specifiedby the manufacturer. Thus, in some embodiments, the water content iswithin the range of from about −30% of the lowest value specified by themanufacturer specifications and +30% of the greatest value specified bythe manufacturer specifications, based upon the weight of the wateradded to the cement before the addition of the colloidal amorphous orother silica described herein.

Yet another benefit of the present invention follows from the ability offormulations thereof to retain water for the benefit of extendedhydration without the formation of capillaries and void reservoirs. Itis known in the art that the addition of aggregate, sand and othercommonly included bulking and strengthening materials to cement to formconcrete generally require additional water to accommodate them in theconcrete and can actually promote the formation of capillaries and,especially, void reservoirs. Such reservoirs are associated with andlocated in relation to the surfaces of the included materials. Ingeneral, the most preferred aggregates and materials are of a qualitysuch that they associate closely with the concrete over their surfaceareas such that during hydration, reservoir formation is minimized, asis the associated loss of compressive strength. However, such highquality included materials are generally uneconomical. Surprisingly,even in the presence of aggregates, the inclusion of amorphous silicaparticles can reduce or prevent the formation of void reservoirs andcapillaries. Without desiring to be bound by theory, the reduction ofsuch imperfections, particularly void reservoirs, and the associatedincrease in compressive strength, tends to indicate that the highsurface area amorphous silica particles are participating in a directassociation with the included material, regardless of materialsuboptimal quality. This association may exclude water and strengthenthe attachment of the concrete to the included material.

Yet another benefit of the present invention is that concreteformulations prepared thereof can be pourable and/or workable withoutthe use of so-called “superplasticizers”. Non-limiting examples of suchsuperplasticizers include ligninsulfonate, sulfonated naphthaleneformaldehyde polycondensates, sulfonated melamine formaldehydepolycondensates, polycarboxylate ethers and other superplasticizercomponents whether they are emulsions, dispersions, powders or otherchemical forms. In one embodiment, the concrete formulations of thepresent invention are pourable without the inclusion ofsuperplasticizers and are superplasticizer-free or essentiallysuperplasticizer-free. By “essentially superplasticizer-free”, it ismeant that the superplasticizer content is in trace amounts of less thanabout 0.1% based upon the weight of the cement.

Below is a non-limiting list of admixtures which can be used with thepresent invention. Alternatively, the concrete mixture of the presentinvention can be free of any or all of the below additives, or of otheradditives. The list below is ordered as per ASTM C 494 categories.Included are admixtures that are certified and not certified by ASTMC-494.

Admixtures can be added as a powder or liquid.

-   -   Normal water reducers and retarders (Type A, B, D)    -   Nominal dosage range: 0.5-6 OZ/C    -   Super-Plasticizers: Normal setting and retarding (Type F, G)    -   Nominal dosage range: 2-40 OZ/C    -   Accelerating Admixtures: water-reducing or non-water-reducing        (Type C, E)    -   Nominal dosage range: 2-45 OZ/C    -   Type S admixtures as defined in ASTM C 494:        -   Mid-Range water-reducers and retarders            -   Nominal dosage range: 2-45 OZ/C        -   Corrosion inhibitors    -   Nominal dosage range: 0.25-5 GAL/YD    -   MVRA (Moisture vapor-reducing admixtures)    -   Nominal dosage range: 5-24 OZ/C    -   SRA (Shrinkage-reducing admixtures)    -   Nominal dosage range: 0.25-5 GAL/YD    -   Hydration stabilizers    -   Nominal dosage range: 0.5-24 OZ/C    -   Viscosity modifiers    -   Nominal dosage range: 0.25-8 OZ/C    -   Air-entraining admixtures;    -   Nominal dosage range: OZ as needed to entrain air: 0.1-36 OZ/C    -   Color agents; Liquid and solid    -   Nominal dosage range: 0.1-20 LB/YD

Example 1

Location: Shelbyville, Ind. at the Shelby Materials ready-mix plant.Environmental Conditions: The start time of the pour was 07:30 AM with astarting temperature of approximately 60° F. The ambient temperaturepeaked in the high 80's during the day. The relative humidity rangedfrom 18% to 67%. The wind speed range was from 3 to 13 mph.

Steps and Results:

1—A traditional class A concrete design of 6 bags (564 lbs) cement to 31gallons of water (SSD—Saturated Surface Dry) per cubic yard (9 yardstotal) was used to place a 4-inch thick interior concrete slab with anon-air-entrained concrete. Roughly 12 gallons of water per cubic yardwas added to the Ready-mix, followed by the dry cement mix (564 lbs peryard) as well as the aggregate and sand (1250 lbs of sand, and 1750 lbsof Stone per yard). The water and dry components were mixed for 1-2minutes, and roughly 19 gallons of additional water per yard was thenadded to the Ready-mix. The mixture was mixed (in a concrete drum thathas a high speed of 12-15 rpm for mixing of the concrete) for anadditional time of 5-10 Minutes. When the driver was ready to transportthe concrete to the job location he then slowed the concrete barrel to3-5 rpm.2-380.7 total ounces of E5 INTERNAL CURE (7.5 ounce/100 lbs cement) werethen added after the 9 yards loaded and batched. Again, there were 564lbs cement and 31 gallons of water per cubic yard.3—The team allowed the ready-mix driver to mix the batch for 5 minutesat 12-15 rpm.4—The ready-mix was then slowed to 2-5 rpm and driven 15 minutes to thejob site. The concrete was then poured into the slab forms. The slablocated against a metal building.5—The traditional finishing process took place. After the pour, the slabwas leveled. A bull float was then used to close the surface. Once thesurface is hard enough to begin the mechanical finishing processappropriate methods used widely in the art were used to complete thefinishing.6—During the bull floating process, it was noted that the concrete wasmuch easier to close than that of a traditional ready-mix process.7—During the finish process where bleed water is generally present, thisprocess presented no bleed water. However, the surface remained moist.The team speculated that unlike concrete prepared from traditionalready-mix products, the water, surprisingly, was retained within theconcrete surface under conditions which would, with ready-mixes in theabsence of E5 INTERNAL CURE, likely give a much drier surface.8—The team then spent 4 hours completing the concrete finishing process.Unlike concrete prepared from traditional ready-mixes, the finishingprocess could be performed with the machines running at half throttlebecause of the moisture still present at the concrete surface. This leadto a much easier finishing process. Traditional concrete requiresmachines to be run at a throttle of 100% and is a more labor-intensiveprocess involving an increased risk of surface damage during finishing.9—The team also noted that the internal thermal temperature swing was inexcess of 50° F. In fact, because the pour was located against a metalbuilding, the internal concrete temperature swing as measured byinternal sensors was from a daytime high of 145° F. to a night time low70° F. In the experience of the team, these temperature swings would beexpected to result in significant cracking of the concrete during curing(see 10, below). In the vast experience of the team, thermaltemperatures are generally one of the greatest accelerators to theevaporation of moisture at the surface of concrete. The day of this pourthe team noticed that the moisture remained at the surface and seemedrelatively unaffected by the thermal temperature swings. The team knewsuch behavior was entirely different than that of traditional pouredconcrete and could be extremely useful in the industry.10—In the experience of the team, traditional concrete would normallyrequire saw cutting within 24 hours of the pour. However, the team didnot saw cut because of the increased amount of water clearly retained inthe upper surface of the concrete and the likelihood that as a result,the shrinkage timing (time over which shrinking would normally occur)would be decreased and likely reduce cracking. Therefore, the concreteslab was allowed to remain undisturbed so that the team could determinehow long it would take for the slab to internally release. To thesurprise of the team, the slab did not internally release itself for 10days. It should be noted that there were significant environmentalchanges such as temperature and rain. Without desiring to be bound bytheory, the team surmised that the addition of E5 INTERNAL CURE wascausing much of the water to be retained, likely through chemicalassociation with the amorphous silica in E5 INTERNAL CURE, rather thanlost through evaporation. It is further surmised that much of theretained water ultimately participated in hydration to give internalcuring. The retention of water through chemical association withamorphous silica in E5 INTERNAL CURE (added to concrete prior topouring, such as, for example to the ready-mix truck), to be laterincorporated through hydration (internal curing), has not been observedbefore, as can best be determined by the team.

Example 2

This was done to ensure consistency in the performance of the productand to understand the process for maximum effect of internal cure.Location: Beach Grove, Ind. at the Shelby Materials ready-mix plantTimeframe: poured between 08:30 am and 09:35 am.Environmental Conditions: 79° F., relative humidity ranged from 61% to93%, cloudy and wind speed ranged from 6.9 to 12.7 mph.

Steps and Results:

1—The concrete for two samples was 5.5 bags (517 lbs) of cement, 0.5water to cement ratio (31 gallons of water (SSD—Saturated Surface Dry)non-air entrained, 5.5 inch slump (517 lbs. of cement, 1225 lbs. ofSand, and 1800 lbs. of Stone per yard). The finishing process was thesame as that of Example 1.2—Sample 1 was poured as a reference. Sample 1 was done and placed as a4″ thick slab. The concrete slab was also cured by applying plasticsheeting on top of the slab for 7 days as recommended by the AmericanConcrete Institute (ACI). The compressive strength was measured 7 daysafter pouring to be 5760 psi.3—Sample 2 was poured as with Sample 1, but with the addition, aftermixing of cement, aggregate and sand, (517 lbs. of cement, 1225 lbs. ofSand, and 1800 lbs. of Stone per yard) of E5 INTERNAL CURE (3.5 oz per100 lbs. of cement). It was cured as Sample 1. 7 days after pouring, thecompressive strength was measured to be 6580 psi. The difference betweensample 1 and 2 (with E5 INTERNAL CURE) was a 14% increase in strength.4—The team of professionals then did a 28-day strength test asrecommended by ACI (American Concrete Institute) to further support theidea that E5 INTERNAL CURE promoted internal curing, thus chemicallybinding the water to the concrete. The 28-day test results were asfollows: Reference compressive strength: 6910 psi. Compressive strengthwhen E5 INTERNAL CURE is included in the poured concrete: 8040 psi. TheE5 INTERNAL CURE increases the compressive strength psi by 16%.

Example 3

Sixteen industrial-scale batches of concrete were prepared. Cylindersfrom each sample were taken and tested for compression strength inaccordance with ASTM C-39, at 3, 7 and 28 days. All samples included1350 lbs sand. For all samples, the Ready-mix was driven an average of20 minutes to the job site, and concrete test cylinders were then pouredin accordance with ASTM C-39. The results are given in Table 1.

The first group of four (samples 1-4), the “Concrete Control” group, areprepared without the addition of colloidal silica. Water/Cement ratio of0.51. They were prepared by adding roughly 40% of the indicated water toa Ready-mix which was rotating at 2-5 rpm, followed by the addition ofthe total indicated quantities of cement mix, aggregate and sand. Theaggregate in all samples in the study was (¾″ #8 ASTM C-33 #8 INDOTapproved) gravel. The water and dry components were mixed for 1-2minutes, which includes the time it took to add the components to theReady-mix drum. The remaining water (approximately 60% of the waterindicated) was then added to the Ready-mix. The mixture was mixed in aconcrete drum that has a high speed of 12-15 RPM's for mixing of theconcrete) for an additional time of 5-10 Minutes. When the driver wasready to transport the concrete to the job location he then slowed theconcrete barrel to 3-5 RPM's. The Ready-mix was driven to the job site,and concrete test cylinders were then poured in accordance with ASTMC-39.

The second group of four (Samples 5-8) are prepared with the addition of4 oz of a colloidal silica solution (E5 Internal Cure: approximately 15wt % silica, average particle size of less than 10 nm, with a BETsurface area of approximately 550 m²/g, and 85 wt % water) perhundredweight cement (cwt).

The procedure for samples 7 and 8 (4 oz/cwt after tail water) is thesame as for samples 1-4, but, additionally, 4 oz/cwt E5 Internal Curewere then added after the barrel was slowed to 3-5 rpm. The Ready-mixmixed the batch for about 5 minutes at 12-20 rpm. The Ready-mix wasslowed to 3-5 rpm and driven to the job site, and concrete testcylinders were then poured in accordance with ASTM C-39.

The procedure for samples 5 and 6 (4 oz/cwt before tail water) was asfor samples 1-4, except that E5 Internal Cure was included in theinitial concrete mix, and the order of addition was cement mix,aggregate/sand, 4 oz/cwt E5 Internal Cure, 40% of water.

The procedure for Samples 9-12 (2, 4, 6 and 8 oz/E5 Internal Cure/cwtbefore tail water; W/C=0.4 l) is the same as that for Samples 6 and 7.Note that the amount of E5 Internal Cure increases for each sample, andthe water/cement ratio is not 0.51, as with samples 1-8, but 0.41.

The procedure for Samples 13-16 (2, 4, 6 and 8 oz/E5 Internal Cure/cwtafter tail water; W/C=0.41) is the same as that for Samples 7 and 8.Note that the amount of E5 Internal Cure increases for each sample, andthe water/cement ratio is not 0.51, as with samples 1-8, but 0.41.

For each sample, the compressive strength was measured from cylindersaged to 3, 7 and 28 days. Note that the compressive strength measuredfor groups of similar samples (1-4; 5 and 6; 7 and 8; 9-12; 13-16)reflect a natural spread which is the result of variations in manyfactors which prevent the samples from being perfectly identical. Thesamples are ordered in order of ascending compressive strength only forconvenience.

In every case in which the silica was added after the tailwater, theconcrete showed little, if any bleedwater, curling, cracking orshrinkage. The same amount of silica added prior to the water gave acement which had a bleedwater amount which was similar to the control,or in some cases, worse than the control. The foregoing held true forboth water/cement ratios (0.51 and 0.41). The compressive strengthgenerally showed an increase with the use of the silica, with moresilica giving a higher increase in compressive strength. However, thepost-tail water addition gave a significantly larger increase than thepre-water addition of the silica. This advantage is in addition to theearlier-noted advantage of greatly reduced bleedwater and curlingcracking and shrinkage. Without desiring to be bound by theory, it isthought that the silica, when added after the water has been mixed withthe other dry components, can reduce the water evaporation from theupper layers more efficiently than if it is added to the dry componentsprior to the water, or possibly even to insufficiently mixed concretemix which contains water. Thus, the examples above illustrate thatadding the silica to a well-mixed and wetted concrete mix, particularlyafter the addition of the tailwater, unexpectedly gives an unexpectedlylarge improvement in compressive strength, as well as less or nobleedwater, and fewer or no defects associated with high evaporationfrom the exposed upper surface of the curing concrete.

We claim: 1) A process for the preparation of a concrete installation,said process comprising the steps of: A) creating a concrete mix fromcomponents, said components comprising each of the following: a) aquantity of dry cement mix, said cement mix characterized by: i) amanufacturer suggested water/cement ratio value; wherein said suggestedratio falls in the range of from about 3.5 to about 6.5; and whereuponcombination with b), the water/cement ratio is greater than the valuecorresponding to about 10% less than the suggested value and not greaterthan the value corresponding to about 30% greater than the suggestedvalue; or ii) manufacturer suggested water/cement ratio range, having anupper value and a lower value, and whereupon combination with b) below,the water/cement ratio is greater than the value corresponding to about10% less than of the lower value and less than the value correspondingto about 30% greater than the upper value; or iii) an amount such that,whereupon combination with b) below, the water/cement ratio is in therange of from about 0.35 to 0.65; b) a quantity of water, c) a quantityof amorphous silica in the range of from about 0.1 to about 7.0 ouncesper hundredweight of cement in a); wherein the average silica particlesize is in the range of from 1 to 55 nanometers and/or wherein thesurface area of the silica particles is in the range of from about 300to about 900 m²/g; d) a quantity of aggregate and/or a quantity of sandin the range of from about 400 to about 700 wt % bwoc; and B) whereinthe water of b) is added in its entirety or in portions comprising aninitial portion, comprising at least about 20 wt % of the quantity ofwater, and a tailwater portion; wherein the initial portion of water iscombined with a) and the components of d) to form a first mix; andwherein the amorphous silica is added to a mix comprising a), d) and theinitial portion of b) to form a second mix; AND wherein the tailwateris 1) added to the first mix or 2) added to the second mix; or 3) isco-added with the amorphous silica to the first mix, wherein theamorphous silica and the tailwater are, optionally, added optionallyintercombined; and wherein 1) the first mix is agitated for a time t₁₁prior to the addition of the tailwater, for a time t₁₂ after theaddition of the tailwater but before the addition of the amorphoussilica, and for a time t₁₃ after the addition of the amorphous silica;or 2) the second mix is agitated for a time t₂₁ prior to the addition ofthe amorphous silica, for a time t₂₂ after the addition of the amorphoussilica but before the addition of the tailwater, and for a time t₂₃after the addition of the tailwater; or 3) the second mix is agitatedfor a time t₃₁ prior to co-addition of the amorphous silica and thetailwater, and whereupon the concrete mix is then agitated for a timet₃₂; OR C) wherein the quantity of water is added to a) and thecomponents of d) to form a mix, whereupon said mix is agitated for atime t_(a) prior to the addition of the amorphous silica, whereupon theconcrete mix is then agitated for a time t_(b); D) pouring the concretemix of B) or C) to form a concrete installation. 2) A process as inclaim 1 wherein the initial portion of water comprises at least 30, 40,50, 60, 70, 80, 90, or 99 wt % of the quantity of water. 3) A process asin claim 1, wherein upon combination of the dry cement mix of a) withthe water of b), the water/cement ratio is: equal to or greater than thesuggested value in i), but less than the value corresponding to 30%greater than the suggested value; or equal to or greater than the uppervalue of the suggested range in ii), but not greater than the valuecorresponding to 30% greater than the upper value; or with respect toiii) at least 0.35, but not greater than 0.65. 4) A process as in claim1 wherein the amorphous silica is introduced into the first mix as acolloidal silica solution and wherein the solution comprises betweenabout 50 and about 95 wt % silica, and between about 5 to about 50 wt %water. 5) A process as in claim 4 wherein the silica comprises betweenabout 75 and about 90 wt % silica and between about 10 and about 25 wt %water. 6) A process as in claim 5 wherein the amorphous silica is addedin an amount in the range of from about 2.5 to about 5.5 ounces perhundredweight cement. 7) A process as in claim 6 wherein the amorphoussilica is added in an amount in the range of from about 3.5 to about 4.5ounces per hundredweight cement. 8) A process wherein the colloidalsilica is added after the tailwater. 9) A process as in claim 1 whereinthe concrete is poured into slab or a footing. 10) A process as in claim1 or 4, wherein the process is conducted in a Ready-mix; wherein thetailwater is added to the first mix after the first mix is agitated at aspeed in the range of from about 2 rpm to about 18 rpm for a time in therange of from 15 seconds to 5 minutes; wherein after the tailwateraddition, the mix is agitated at a speed in the range of from about 5rpm to about 18 rpm, for a time in the range of from about 1 minute toabout 18 minutes, after which the silica is added, as colloidal silica,to the Ready-mix, and the mix is agitated for a time in the range offrom about 1 to about 15 minutes at a speed in the range of from about 2to about 18 rpm; wherein the concrete is then poured as a slab form.